### Introduction

Many linguistic researchers are interested in *semasiological* variation, that is, how the meaning of words and expressions may be observed to vary over time or space. One word might have one dominant meaning or use at one point in time, and other meanings may supplant them. This is of obvious interest to etymology. How do new meanings come about? Why do others decline? Do old meanings die away or retain a specialist use?

Most of the research we have discussed on this blog is, by contrast, concerned with *onomasiological* variation, or variation in the choice of words or expressions to express the same meaning. In a linguistic choice experiment, the field of meaning is held to be constant, or approximately so, and we are concerned primarily with language production:

- Given that a speaker (or writer, but we take speech as primary) wishes to express some thought,
*T*, what is the probability that they will use expression*E*₁ out of the alternate forms {*E*₁,*E*₂,…} to express it?

This probability is meaningful in the language production process: it measures the actual use out of the options available to the speaker, at the point of utterance.

Conversely, semasiological researchers are concerned with a **different type** of probability:

- Given that a speaker used an expression
*E*, what is the probability that their meaning was*T*₁ out of the set of {*T*₁,*T*₂,…}?

For the hearer, this measure can also be thought of as the **exposure rate**: what proportion of times should a hearer (reader) interpret *E* as expressing *T*₁? This probability is meaningful to a language receiver, but it is not a meaningful statistic at the point of language production.

From the speaker’s point of view we can think of onomasiological variation as variation in *choice*, and semasiological variation as variation in *relative proportion of use*.